Non-contact power feeding to movable objects such as transportation vehicles in a manufacturing plant, elevators and the like achieves to eliminate such problems as contact wear or sparks that are common to a trolley type power feeding or cable retention or entangling problems in cable power feeding, thereby simplifying maintenance. This is one of the reasons why non-contact power feeding devices are developed and put into practical use in recent years by applying the transformer principle, wherein an electrical power is supplied to a primary winding of a transformer and power is induced in a secondary winding by the electromagnetic induction for feeding power in a non-contact manner.
FIG. 25 illustrates a device that is developed for non-contact power feeding to a movable object. This device comprises an alternating current (AC) power supply that outputs an AC power having the frequency f0, a power feeding line 5 disposed along the path of the movable object and acting as a primary winding of a transformer, a capacitor Cp1 that constitutes a parallel resonance circuit together with the primary winding and a moving assembly that comprises a pick-up 6 for acquiring power in non-contact relationship from the power feeding line 5, a secondary winding 2 held in the pick-up 6, a (magnetic) core 7 for the secondary winding 2, a load ZL of the moving assembly and a capacitor Cp2 that constitutes a parallel resonance circuit together with the secondary winding 2.
In this power feeder, power is outputted to the power feeding line 5 from the AC power supply and supplied to the load ZL of the moving assembly by way of the secondary winding 2 that is a non-contact relationship with the power feeding line 5.
Alternatively, FIG. 26 illustrates a stationary (non-moving) non-contact power feeder that is employed in a charger for codeless household electrical appliances and cellular phones. In this power feeder, a core 7 is provided for winding each of the primary winding 1 and the secondary winding 2. Power is sent by electromagnetic induction from the primary winding 1 to the secondary winding 2 that is connected to a household electrical appliance and a cellular phone.
FIG. 27 illustrates the moving assembly side in the non-contact power feeder in FIG. 25, further providing a diode rectifier 40 and a smoothing capacitor C for supplying DC power to the load ZL. In this power feeder, an AC output in the secondary winding 2 is converted into a DC power before being supplied to the load ZL.
FIG. 28 illustrates an application of the stationary non-contact power feeder in FIG. 26, wherein a diode rectifier 40 and a smoothing capacitor C are provided at the secondary winding side to be connected to a household electrical appliance or a cellular phone for supplying a DC power to the load ZL.
These non-contact power feeders can be shown in the same equivalent circuit as a transformer. However, since there is an air gap between the primary winding and the secondary winding unlike a closely coupled transformer, the coupling factor is very low and there causes a large leakage inductance. In order to solve the problem, a resonance circuit is used for improving power conversion efficiency in the conventional non-contact power feeders.
Now, a description will be made on the resonance circuit in the conventional non-contact power feeders.
It is to be noted in this specification and drawings that the number of turns of the primary winding is N1, the number of turns of the secondary winding is N2 and the winding ratio n=N1/N2.
FIG. 29 (a) is a circuit configuration of a non-contact power feeder as disclosed in the following Non-patent Document 1. Parallel resonance circuits are provided in both of the primary winding side and the secondary winding side. FIG. 29 (a′) is an equivalent circuit of the circuit in FIG. 29 (a) and the transformer is shown in a T-type equivalent circuit.
It is shown in this equivalent circuit that the angular frequency of the power supply output is ω0 (=2πf0), the primary leakage reactance of the transformer in this instance is x1, the secondary leakage reactance converted to the primary side is x2 and the magnetizing reactance converted to the primary side is x0. Accordingly, if it is assumed that the primary leakage inductance is l1, the secondary leakage inductance converted to the primary side is l2 and the magnetizing inductance (mutual inductance) converted to the primary side is l0, the above x1, x2 and x0 are given by the following (Expressions 1˜3):x1=ω0×l1  (Expression 1)x2=ω0×l2  (Expression 2)x0=ω0×l0  (Expression 3)
On the other hand, xP1 is the capacitive reactance of the primary side capacitor when the angular frequency is ω0 (=2πf0) and xP2 is the capacitive reactance of the secondary side capacitor converted to the primary side in the same condition as mentioned above. Assuming that the capacitance of the primary side capacitor is Cp1 and the capacitance of the secondary side capacitor converted to the primary side is Cp2, xP1 and xP2 are given by the following (Expressions 4 and 5):xP1=1/(ω0×Cp1)  (Expression 4)xP2=1/(ω0×Cp2)  (Expression 5)
If the actual capacitance of the secondary capacitor not converted to the primary side is Cp2′, it is given by the following (Expression 6):Cp2′=n2×Cp2  (Expression 6)
If the magnetizing inductance (mutual inductance) not converted to the primary side is l0′, there exists the relationship of the following (Expression 7):i0=n×l0′  (Expression 7)
If the self inductance of the primary winding is L1 and the self inductance of the secondary winding not converted to the primary side is L2, there are the relationship as given by the following (Expressions 8 and 9):l1=L1−l0  (Expression 8)l2=(n2×L2)−l0  (Expression 9)
Where, n is the winding ratio. If the winding ratio n=1, the value not converted to the primary side and the value converted to the primary side are equal to each other.
In the system of the Non-patent Document 1, circuit parameters are set so that the capacitor in the primary side and the self inductance of the primary inductance form a resonance circuit (in such a manner that xP1=x0+x1) and similarly, the capacitor in the secondary side and the self inductance of the secondary winding form a resonance circuit (in such a manner that xP2=x0+x2).
FIG. 29 (b) shows a circuit arrangement to eliminate the resonance circuit in the primary side by using as a power supply a current source that outputs a current of the frequency f0 as is the case in a current type inverter. FIG. 29 (b′) shows its equivalent circuit, wherein x1, x2, x0 and xP2 have the same meaning as those in FIG. 29 (a′).
Alternatively, FIG. 29 (c) shows a circuit arrangement of a non-contact power feeder as disclosed in the following Non-patent Document 2. FIG. 29 (c′) shows its equivalent circuit. This power feeder has a capacitor in the secondary side having the capacitance Cs2 converted to the primary side. The capacitive reactance xS2 of the secondary side capacitor converted to the primary side has the relationship with Cs2 given by the following (Expression 10) when the angular frequency of the power supply output is ω0 (=2πf0):xS2=1/(ω0×Cs2)  (Expression 10)
If the capacitance of the actual secondary side capacitor not converted to the primary side is Cs2′, there exists the following (Expression 11):Cs2′=n2×Cs2  (Expression 11)It is to be noted that x1, x2 and x0 in FIG. 29 (c′) have the same meaning as those in FIG. 29 (a′).
In the system as disclosed in the Non-patent Document 2, the magnetizing reactance x0 is neglected and the capacitance Cs2 is provided so that the primary leakage reactance x1, the secondary leakage reactance x2 and the secondary side capacitor form a series resonance circuit (that is, xS2=x1+x2).
FIG. 29 (d) shows a circuit arrangement of a non-contact power feeder as disclosed in the following Patent Document 1 and FIG. 29 (d′) shows its equivalent circuit. Note that x1, x2, x0, xP1 and xS2 in FIG. 29 (d′) have the same meaning as those in FIG. 29 (a′) and FIG. 29 (c′).
In the system of the Patent Document 1, the magnetizing reactance x0, the secondary leakage reactance x2 and the secondary side capacitor Cs2 form a series resonance circuit (that is, 1/(ω0×Cs2)=xS2=x0+x2) and moreover the capacitance of the Cp1 is chosen so that the series resonance circuit is tuned with the basic frequency of the power supply output.
In this equivalent circuit, since 1/(ω0×Cs2)=x0+x2, if the load is a resistance R (ZL=R), the impedance ZA of the circuit portion at the right of the line AA′ in FIG. 29 (d′) is given by the following (Expression 12):ZA=x02/R+j(x0+x1)  (Expression 12)Moreover, there is a description in the Patent Document 2 that if the ZA is converted into a parallel circuit of a combined load resistance R″ and a combined inductance and the capacitance of the Cp1 is chosen to form a parallel resonance circuit together with the parallel circuit, the entire circuit including the Cp1 can be converted into a simple equivalent circuit and the combined load resistance R″ is given by the following (Expression 13):R″=R(x0+x1)2/x02  (Expression 13)
However, as will be described hereinafter, the above (Expression 13) excludes x02/R.
Patent Document 1: JPA-2002-320347
Non-patent Document 1: A. W Green and J. T. Boys, “10 kHz Inductively Coupled Power Transfer-Concept and Control”, Power Electronics and Variable-Speed Drives, 26-28 Oct., 1994, Conf. Publication No. 399, IEE
Non-patent Document 2: Ayano, Nagase and Inaba, “Studies on High Efficiency Non-contact Power Feeder”, Electric Academy Papers D, Vol. 123, No. 3, 2003